Select multiple dates with DatePicker

Question

I am trying to create a DatePicker that selects multiple dates. I am able to select multiple dates but I would like to keep the DatePicker open while I select them. Proble

Answer 1

If you check DatePickerContent class, you can find that each time a new DateCell is created, an EventHandler of type MOUSE_CLICKED is added to it. This handler will call selectDayCell(DateCell) when the user clicks on a cell. selectDayCell(DateCell) sets the new date value and hides the DatePicker:

protected void createDayCells() {
    final EventHandler<MouseEvent> dayCellActionHandler = ev -> {
        if (ev.getButton() != MouseButton.PRIMARY) {
            return;
        }
        DateCell dayCell = (DateCell)ev.getSource();
        selectDayCell(dayCell);
        lastFocusedDayCell = dayCell;
    };
    for (int row = 0; row < 6; row++) {
        for (int col = 0; col < daysPerWeek; col++) {
            DateCell dayCell = createDayCell();
            dayCell.addEventHandler(MouseEvent.MOUSE_CLICKED, dayCellActionHandler);
            dayCells.add(dayCell);
        }
    }
    dayCellDates = new LocalDate[6 * daysPerWeek];
}

public void selectDayCell(DateCell dateCell) {
    datePicker.setValue(dayCellDate(dateCell));
    datePicker.hide();
}

If you're using Java 9 or newer, you can extend DatePickerContent class and override the selectDayCell(DateCell) method to not hide the DatePicker after a cell is selected:

public void selectDayCell(DateCell dateCell) {
    datePicker.setValue(dayCellDate(dateCell));
}

Unfortunately, in Java 8, DatePickerContent has a package-private constructor so you can't extend from it. As a workaround, you can add another EventHandler on mouse click that will show the DatePicker again after a cell is clicked:

EventHandler<MouseEvent> mouseClickedEventHandler = clickEvent -> {
    if (clickEvent.getButton() == MouseButton.PRIMARY) {
        datePicker.show();
    }
    clickEvent.consume();
};

In your cell factory:

@Override
public void updateItem(LocalDate item, boolean empty) {
    super.updateItem(item, empty);
    //...
    if (item != null && !empty) {
        //...
        addEventHandler(MouseEvent.MOUSE_CLICKED, mouseClickedEventHandler);
    } else {
        //...
        removeEventHandler(MouseEvent.MOUSE_CLICKED, mouseClickedEventHandler);
    }
}

Answer 2

Using M. S. answer, I was able to create this for JavaFX8 :

public class MultiDatePicker
{

    private static final DateTimeFormatter DATE_FORMAT = DateTimeFormatter.ofPattern("yyyy-MM-dd");
    private final ObservableSet<LocalDate> selectedDates;
    private final DatePicker datePicker;

    public MultiDatePicker()
    {
        this.selectedDates = FXCollections.observableSet(new TreeSet<>());
        this.datePicker = new DatePicker();
        setUpDatePicker();
    }


    public ObservableSet<LocalDate> getSelectedDates()
    {
        return this.selectedDates;
    }

    public DatePicker getDatePicker()
    {
        return this.datePicker;
    }

    private void setUpDatePicker()
    {
        this.datePicker.setConverter(new StringConverter<LocalDate>()
        {
            @Override
            public String toString(LocalDate date)
            {
                return (date == null) ? "" : DATE_FORMAT.format(date);
            }

            @Override
            public LocalDate fromString(String string)
            {
                return ((string == null) || string.isEmpty()) ? null : LocalDate.parse(string, DATE_FORMAT);
            }
        });

        EventHandler<MouseEvent> mouseClickedEventHandler = (MouseEvent clickEvent) ->
        {
            if (clickEvent.getButton() == MouseButton.PRIMARY)
            {
                if (!this.selectedDates.contains(this.datePicker.getValue()))
                {
                    this.selectedDates.add(datePicker.getValue());

                } else
                {
                    this.selectedDates.remove(this.datePicker.getValue());

                    this.datePicker.setValue(getClosestDateInTree(new TreeSet<>(this.selectedDates), this.datePicker.getValue()));

                }

            }
            this.datePicker.show();
            clickEvent.consume();
        };

        this.datePicker.setDayCellFactory((DatePicker param) -> new DateCell()
        {
            @Override
            public void updateItem(LocalDate item, boolean empty)
            {
                super.updateItem(item, empty);

                //...
                if (item != null && !empty)
                {
                    //...
                    addEventHandler(MouseEvent.MOUSE_CLICKED, mouseClickedEventHandler);
                } else
                {
                    //...
                    removeEventHandler(MouseEvent.MOUSE_CLICKED, mouseClickedEventHandler);
                }

                if (selectedDates.contains(item))
                {

                    setStyle("-fx-background-color: rgba(3, 169, 244, 0.7);");

                } else
                {
                    setStyle(null);

                }
            }
        });

    }

    private static LocalDate getClosestDateInTree(TreeSet<LocalDate> dates, LocalDate date)
    {
        Long lower = null;
        Long higher = null;

        if (dates.isEmpty())
        {
            return null;
        }

        if (dates.size() == 1)
        {
            return dates.first();
        }

        if (dates.lower(date) != null)
        {
            lower = Math.abs(DAYS.between(date, dates.lower(date)));
        }
        if (dates.higher(date) != null)
        {
            higher = Math.abs(DAYS.between(date, dates.higher(date)));
        }

        if (lower == null)
        {
            return dates.higher(date);
        } else if (higher == null)
        {
            return dates.lower(date);
        } else if (lower <= higher)
        {
            return dates.lower(date);
        } else if (lower > higher)
        {
            return dates.higher(date);
        } else
        {
            return null;
        }
    }

}